The present invention relates to an apparatus and method for manufacturing a liquid crystal display used for an image display panel of a computer apparatus, a television set, etc.
FIG. 6 is a drawing schematically showing a cross section of a liquid crystal display. As shown in the drawing, the liquid crystal display 10 comprises a lower substrate 12 made of a transparent material (such as glass), an upper substrate 14 formed equally by a transparent material, and a liquid crystal material 16 held between the lower substrate 12 and the upper substrate 14. Although not shown in FIG. 6, electrodes are formed on surfaces of the lower substrate 12 and the upper substrate 14. The lower substrate 12 and the upper substrate 14 are bonded to each other by an adhesive 18 applied continuously along peripheral edge portions of the lower substrate 12 and the upper substrate 14. The adhesive 18 contains ball-like spacers 20 each having a certain diameter of about 5 xcexcm, for example. This results in a constant gap, normally identical to the diameter of the spacing balls, between the lower and upper substrates 12 and 14.
The liquid crystal display 10 is manufactured through steps shown in FIGS. 7A to 7D. Specifically, the adhesive 18 capable of being hardened by the exposure of an ultraviolet ray is applied continuously along a peripheral edge portion of a top surface of the lower substrate 12 (FIG. 7A). Although not shown in the drawing, the adhesive 18 contains the spacers 20 shown in FIG. 6. A typical thickness of the adhesive 18 applied to the substrate 12 is about 30 xcexcm. Then, the liquid crystal material 16 is dropped evenly within an area of the top surface of the lower substrate 12, defined by the adhesive 18 (FIG. 7B). Subsequent to this, the lower substrate 12 together with the liquid crystal material 16 is placed on a lower drawing station 24 through an elastic sheet 22 interposed in between (FIG. 7C). The upper substrate 14 supported by an upper drawing station 28 is thereafter lowered toward and pressed onto the lower substrate 12 in a vacuumed atmosphere 26. This causes the liquid crystal material 16 to extend in all directions between the substrates 12 and 14. The lower drawing station 24 is thereafter moved in the horizontal direction, to thereby correctly position the lower substrate 12 with respect to the upper substrate 14. In this condition, the upper drawing station 28 together with the upper substrate 14 is further descended, so that a pressure is applied until the gap between the lower and upper substrates 12 and 14 reaches a predetermined value substantially equal to the diameter of the spacers. At last, the adhesive 18 is exposed to an ultraviolet ray 32 irradiated from an ultraviolet lamp 30, so that it is hardened (FIG. 7D) to complete the liquid crystal display 10.
However, in the conventional apparatus for manufacturing a liquid crystal display, the elastic sheet 22 disposed between the lower substrate 12 and the lower drawing station 24 includes a number of small voids. Disadvantageously, each void expands in the vacuumed atmosphere 26. As a result, when biasing the upper substrate 14 to the lower substrate 12, the expanded voids causes an unwanted horizontal movement of the lower substrate 12 relative to the upper substrate 14 that has been correctly positioned to the other in the previous positioning stage.
Accordingly, an object of the present invention is to provide an apparatus and method for manufacturing a liquid crystal display, which prevents a lower substrate or an upper substrate from moving from the other while the upper substrate is pressed against the lower substrate, and thereby allows to obtain a liquid crystal display in which a lower substrate is correctly positioned with respect to an upper substrate.
To this end, an apparatus for manufacturing a liquid crystal display includes a lower drawing station disposed below the lower substrate and movable in the horizontal direction. The lower drawing station has a surface portion opposed the lower substrate and formed with a plurality of suction holes therein. An upper drawing station disposed above the upper substrate has a surface portion opposed the upper substrate and formed with a plurality of suction holes therein. An elastic sheet is provided between the lower substrate and the lower drawing station and/or between the upper substrate and the upper drawing station. Advantageously, the elastic sheet is made of member in which substantially no isolated void is enclosed therein. Examples of the material of the elastic sheet are silicon or fluorine material.
According to the present invention, the elastic sheet positioned between the substrate and the drawing station presents substantially no expansion in a vacuum. This allows the elastic sheet to deform only in the biasing direction (i.e., vertical direction) but not in another direction (i.e., horizontal direction) perpendicular to the biasing direction when it is pressed between the upper and lower substrates. Therefore, a positional relationship (i.e., horizontal relationship) between the upper and lower substrates, which has been determined in the previous stage, is maintained in the subsequent process made in the vacuum and also in the final product.
In another aspect of the present invention, the elastic sheet has a plurality of through-holes extending through the elastic sheet. This allows the vacuum to be applied through the elastic sheet to the adjacent substrate, preventing the movement of the substrate relative to the drawing station.
In addition, a method for manufacturing a liquid crystal display includes
providing a lower drawing station having a lower support surface;
positioning an elastic sheet on the lower support surface, the lower elastic sheet being made of a void-free member in which substantially no independent void communicated to the atmosphere is included therein;
drawing the elastic sheet to the lower drawing station;
positioning a lower transparent substrate on the lower elastic sheet;
positioning a liquid crystal material on the lower transparent substrate;
providing an upper drawing station having an upper support surface;
positioning an upper transparent substrate on the upper support surface;
drawing the upper transparent sheet to the upper drawing station; and
in a vacuum, moving the upper drawing station toward the lower drawing station so that the upper transparent substrate contacts with the liquid crystal material positioned on the lower transparent substrate and thereby the liquid crystal material is extended between the lower and the upper substrates.